r gurtler



Sept. 6, 1932 FT GURTLER 1,876,451

IRON CORED INDUCTANCE (CHOKE COIL, TRANSFORMER) FOR DIRECT CURRENT LOADS Filed July-11. 1951 2 Sheets-Sheet 1 INVENTOR who '6 LEE BY m,

ATTORN EY Sept. 6, 1932 GURTLER 1,876,451

IRON CORED INDUCTANCE (CHOKE COIL, TRANSFORMER) FOR DIRECT CURRENT LOADS Filed July 11, 1931 2 Sheets-Sheet 2 & F I Illllllll! 1 259. a III .10 @9 4 129.12

IuLI

INVENTOR RUDOLF a ILER ATTORNEY Patented Sept. 6, 1932 UNITED STATES PATENT OFFICE RUDOLF GURTLEB, OF BERLIN, GERMANY, ASSIGNOIt T TELEFUNKEN GESELLSCHAFT FUR DRAHTLOSE TELEGRAPHIE M. B. 31., OF BERLIN, GERMANY, A CORPORATION OF GERMANY IBON-COBED INDUCTANCE (CHOKE COIL, TRANSFORMER) FOR DIRECT CURRENT LOADS Application filed July 11, 1931; Serial No.

This invention relates to electric inductance apparatus and the like and more particularly to novel methods of controlling t e magnetic reluctance of cores used in electrical work.

The objects of the invention will be apparent from the following specification when read in connection with the appended drawings, wherein,

Fig. 1 shows a core of the shell type with a winding;

Fig. 2 illustrates curves utilized in describing the invention;

Fig. 3 shows diagrammatically another form of core construction;

Fig. 4 illustrates a core in which two air gaps are provided;

Fig. 5 is a diagrammatic showing of conditions existing in a core wherein an air gap is rovided partly through the core;

Figs. 6 and 7 illustrate cores wherein the cross-section has been reduced;

Fig. 8 illustrates a shell type core with the cross-section along certain portions of the core reduced;

Fig. 9 illustrates diagrammatically another type of core; and,

Figs. 10, 11 and 12 illustrate in a diagrammatic manner various constructions of cores contemplated by the invention.

It is known that the inductance of an ironcored coil (choke-coil or transformer) decreases to a small value in the presence of D. C. loads. But if an air-gap is provided in the iron-core as illustrated, for instance, in Figs. 1 and 3, it is possible to increase the inductance for D. C. loads. Fig. 2 roughly illustrates the dependence of the self-inductance of a iven choke-coil upon the D. C. Graph a re ers to a choke-coil comprising a closed iron-core (stratified or superposed sheets or laminations), b to a choke-coil with l =0.5 mm. air-gap, 0 to l =1.5 mm. It will be seen from the curves that in the presence of a D. C. of 50 milliamps, and an air-gap of mm., shows maximum inductance, while for a D. C. of 100 milliamps, the gap must be 1.5 mm. in order that maximum inductance and thus optimum utilization may be insured. This size of air-gap therefore shall be called 5 the optimum ga 550,118, and in Germany August 14,, 1930.

L oAnm i x 10- henry if n=number of turns R1=reluctance of iron path (for A. C.)

R2=reluctance of air-gap.

There is furthermore:

where Z =mean iron-path gl=iron cross-section ipermeability for A. G. flux, in the presence of a given D. C. ats load of the iron.

This A. C. flux permeability a (also known as incremental permeabilit is a marked function of the D. C. ats. hen the latter increase ,1 decreases, as borne out by graph a, Fig. 2, since the inductance is proportional to with a closed iron-core or path, the purpose of the reluctance R2 (airgap), as will now be seen is to absorb a large part of the aggregate D. ats, and as a result the iron will have far less ats per centimeter and exhibit a far higher incremental permeability As a result the magnetic reluctance of the iron path decreases so markedly that in spite of the added air-gap reluctance R the total reluctance R +R is then considerably lower than R alone previously. (Cf, for instance, L of graphs a and c, Fig. 2, for 100 milliamps). But if R2 becomes too large, a decrease of R1 will do no good any more, for the total reluctance R1+R2 will grow. Hence, there is acertain air-gap width, i. e., the optimum width for which R1+R2 is of a minimum value and thus L a maximum.

If this fact were left out of consideration, then, in order to obtain a certain required inductance, there would result several times more material, wei ht, labor and cost.

For this reason it is extremel important to choose the optimum airap or the core. Where relatively large-size types of chokecoils and transformers are concerned, it is generally speaking not diilicult to provide the optimum air-gap width being found either by calculation or empirically.

The same problem becomes often difficult and expensive, occasionally even impracticable, where smaller types of choke-coils and transformers are dealt with, most particular- 1y those furnished with cores consisting of high-permeability material. For in these instances there result such small values for the air-gap that they can often not be made at all, for instance, the frequently employed shell-type Fig. 1. In the ease of the core-type, Fig. 3, the provision ofa small air-gap if obtainable at all (for instance, by inter-posing a very thin piece of mica or the like) is attended with such great difiiculties that the discrepancies in inductance between different coils are mostly unduly great.

Now, according to the present invention the above problem is solved in a cheap and simple manner by that the iron-core has no break in the form of a continuous air-gap (Z Figs. 1 and 3), but that the iron-core cross-section is reduced at one or more points. An embodiment of this idea is illustrated in Fig. 4, where the core is cross-sectionally reduced at two points, this end being here attained by suitable superposition or assembly of sheet laminations with an air-gap. Fig. 5 shows the approximateshape or path of the induction lines about the reduced section. But what should be borne in mind is that the major part of the induction lines passes the (admittedly) very short spaces between the laminations. The regulating reluctance R2, as it could be called which in the standard form of construction consists of a longitudinal air-gap (in the direction 9f the mean path through the iron), consists in the disclosure essentially of a transversal air-gap (at right angles to the iron path), and of a portion having a diminished iron cross-section. At this place, of course, the iron permeability is lower than in the rest of the core.

By means of such an arrangement it is possible to insure the desired value in the regulating reluctance R2, a value that can not be exactly attained with small-size chokecoils having the usual air-gap or which would have to be exceeded several times.

A choke-coil corresponding to Fig. 4 comprised 30,000 turns and a core comprising 45 laminations of ordinary transformer sheet material. This coil showed an inductance of 290 henry when provided with a solid core, at a D. C. of 1 milliamp. )Vhen furnished with a core as shown in Fig. 1 having a 03-min. air-ga the inductance is found to be 315 henry. alculation shows that this choke-coil, in the presence of a current of 1 milliamp., exhibits a maximum inductance for an air-gap of 0.07 mm. However even an air-gap of 0.1 mm. cannot be made by punching; and even if it were practicable one would have to calculate with too large tolerance limits. Hence, the choke-coil was furnished with a core as shown in Fig. 4,1:nninations of 0.3-mm. being used, 22 thereof being shifted in the coil body or bobbin in one direction, and 23 in the opposite sense. For such a core the inductance, at 1 milliamp. 1). C. amounted to 400 henry. Hence, by utilizing the basic idea of this invention an improvement of the coil of about 30% was possible.

The usefulness of the invention can be demonstrated still more clearly by the following example: \Vith a core of the same size as in the previous instance a plate choke-coil for 1 milliamp. D. C. and not less than 500 henry was to be made. When completely wound with practically still permissib e thin wire, there were 36,000 turns on the bobbin to be used. For the smallest air-gap that is still permissible in practice of 0.3 mm., there results an inductance of only ca 440 henr (for a D. C. of 1 millamp.). Hence, ordinarily a larger core would have to be used, and this would mean higher cost, expenditure of more material, greater weight, and more space. But if a core as shown in Fig. 4 is taken comprising two reductions in crosssectional area then an inductance of 550 henry was obtained, for 1 milliamp.

This design of the core offers this further merit that a high manufacturing tolerance is permissible. In actual manufacture there suflices the rule that approximately one-half of the sheets to build up a core should be placed in one direction, and the balance in the opposite direction. In case it should then happen that in one direction only 12 instead of 22 are piled up, and in the opposite direction 33 instead of 23, the inductance was found to be at most only 2% lower. Such great tolerance as regards the optimum inductance may be explained from the circumstance that one of the cross-sections (g') is somewhat reduced, and the other one is increased.

Under certain circumstances it may be desirable to constitute the regulating reluctance R2 merely by one iron reluctance, in other words, to reduce the core cross-section at one place by that the lemellze are made narrower at one place. An embodiment is shown in Fig. 6, where a is the core, and b a lamination. The notches or cut-outs can be used in the mounting work.

In what follows a number of other embodiments shall be described to further illustrate the basic idea of the invention.

Fig. 7 shows a longitudinal cross-section at right angles to the lamination surface laid through a core, laminations with air-gap and laminations without air-gap being used for building up the core. The height a is formed by sheets without air-gap which are laid in the usual way staggered (i. e., solid on joint), while the height I) is formed by laminations with air-gap.

Fig. 8 represents a choke-coil with normal and frame laminations. The normal laminations, Fig. 8a, present in this embodiment two grooves e-e, while the frame laminations, Fi 8b, difier from the standard form in that t e tongue is missin Fi 8c is a longitudinal cross-section o the c oke-coil. In addition of a core consisting of a laminations, it has two frames built up of b laminations connected with the core. By means of this design for a given space, a hi h inductance is attainable without undu y many turns being required, for a reater number of turns would mean an undifiy high drop of D. C. potential.

Another instance of a choke-coil comprising one local cross-sectional reduction is shown in Fig. 9. The laminations have a very narrow tongue and are laidstaggeredfashion so that the choke-coil neither has a longitudinal nor a transversal air-gap. R2 is constituted by the tongue of reduced crosssection.

Generally speaking, the reduction in crosssectional area can be effected at any number of points and in various ways, for instance, by the use of different shapes of laminations. Also the sequence in piling up the strata may be different, as shall be explained in what follows by a simple example.

Fig. 10 is a longitudinal section thro h the core of a choke-coil which consists o a lamination without air-gap and a number of laminations with air-gap 1,. The solid or unreduced lamination is laced marginally, though if desired, it coulcl be placed also between the airp laminations, as in Fig. 11.

The manu acture of choke-coils with larger air-gaps could be also simplified by that laminations with a comparatively large air-gap l, are em loyed, while bridging t e same by a sheet ifted in inversely (as, for instance, in Fig. 10) If, then, the reluctance R2 should turn out too low, the bridging lamination m (Fig. 12) is provided with a sufliciently heavy coat of insulation 8, with the result that the transverse air-gap and thus also R2 are augmented.

I claim: a

1. In the manufacture of electrical induction apparatus comprising a magnetic core and at east one windin on said core, said core being constructed 0 laminations of core material, the method of fixin the magnetic reluctance of the apparatus which comprises forming air gaps in enough of said laminations to increase themagnetic reluctance ofthe apparatus to a value sli htly less than the desired value and then urther increasing the value of the magnetic reluctance to the desired value by inserting a layer of in sulation materialbetween at least two adjacent laminations.

2. A core for transformers, choke coils and the like comprising a plurality of laminations some of WhlCh are provided with air gaps, and strips of insulation material between certain adjacent laminations.

3. Electric induction ap aratus comprising a magnetic core adap to have a winding supported thereon, said core being formed of laminations of core material some of which are provided with air gaps and insulation material between said laminations of var ing insulating qualities for determining e magnetic reluctance of the apparatus.

4. In the manufacture of electrical induction apparatus comprising a magnetic core and at least one winding supported on said core, said core being constructed of laminations of core material, the ste s in the method of fixing the magnetic re uctance of the apparatus which com rise forming air ga in enough of said laminations to increase t e magnetic reluctance of the apparatusto a value which is less than that of the desired value and further increas' the value of the magnetic reluctance thereo to more nearly the exact desired value by inserting a layer of insulation material between two adjacent laminations, at least one of which is not provided with an air fia [YDOLF GURTLER.

III 

